SDRAM configuration

[sharanbr]

Hi All,

When a DRAM data sheet specifies
256M X 4 or
128M X 8 or
256M X 16

Does this mean that same SDRAM chip can be used with X4, X8 or X16 mode (i.e. chip has 16 data pins; but we can use 4/8/16 of them) or
these are different chips ?

Thanks,
Sharan

[Will.Spencer]

256M X 4 means that the DRAM is 256 megabits long and 1 bit wide.

128M X 8 means that the DRAM is 128 megabits long and 8 bits wide.

256M X 16means that the DRAM is 256 megabits long and 16 bits wide.

If your CPU's Front Side Bus is 64 bits wide, then you will need to add 64 256Mx1 chips at a time to your system. This would give you 2GB of RAM.

Or, you could add 8 128Mx8 chips; this would give you 1GB of RAM.

Or, you could add 4 256Mx16 chips; this would give you 2GB of RAM.

This has to do with the internal row/column design of the chips, and is not related to the configuration of data pins.

Of course, as most memory comes packaged on DIMM's now, this is somewhat irrelevant to most users.

On your datasheet, you can see how those cannot all be the same chips, because the third example has a much greater capacity than the first example.